The invention is based on device for simultaneous detection of dissimilar gas components, with a number of electrochemical, three-electrode measuring cells (working electrode/counter-electrode/reference electrode) with a common electrolyte and a potentiostatic evaluation circuit for setting and regulating different potentials at the working electrodes, and for measuring the electrochemically-produced electric currents that are correlated with the individual gas concentrations.
Potentiostatic, three-electrode sensors are widely used for the measurement of gases in trace detection through to investigations on pure gases. These gas sensors are usually reproducible, sensitive, and can be made for a number of different gases. The selectivity can be controlled by the choice of catalyst at the measuring electrode, the electrolyte and the potential at the measuring electrode (working electrode). However, not all cross-sensitivities can be eliminated simultaneously. In fact, in practice a compromise has to be found between sensitivity and the suppression of cross-sensitivity with respect to other interfering gases.
Alternatively, several sensors can be combined in a sensor array and the various sensitivities for the sought-for measured components, and the interfering cross-components, are used during processing of the measured variables. The composition of the gas can then be determined (sample detection) by taking all sensor signals into account. In the past such sensor arrays have been based on conductivity-type solid-state gas sensors.
An electrochemical multi-electrode sensor in which the gas flows through successive electrochemical measuring cells, is described in DE 24 35 813. The measuring cells are interconnected via a resistance network that is connected to the electrodes, so that only one measuring voltage related to one specific pollutant is generated in each cell. This requires that a complete reaction takes place in each stage so that longer retention times and thus longer dead times have to be accepted during the measurement. Furthermore, the underlying measurement principle requires that all electrodes are brought out separately for each measuring cell. These characteristics contradict the requirement for a compact electrochemical, multi-electrode of simple construction. Temperature-differences and differing inflow rates in the individual measuring cells must also be taken into account.
Furthermore, potentiostatic, four-electrode sensors for measuring special gas systems are known from U.S. Pat. No. 4,315,753 and Ep 00 64 337. But there is no facility for selecting the potentials of the working electrodes independently of each other. Consequently there is very little freedom for optimizing the selectivities individually. Apart from that, expensive gas control is also necessary to some extent in this state-of-the-art.
The aim of the invention is to measure several gas components simultaneously and independently of each other with the aid of an electrochemical, multi-electrode sensor, whereby with regard to optimization of the selectivity for detection of the individual gas components, full freedom in determining the electrode potential, the choice of electrode material, including catalytic additives, and the use of suitable gas filters and gas diffusion barriers, is provided.